X-Git-Url: https://git.distorted.org.uk/~mdw/sod/blobdiff_plain/9a3cb4610ab59001fd44c13dcdc6ea206acf0e50..a4c0734b7ecd9c7792d7feef8c6b8af3983cfe6d:/src/utilities.lisp

diff --git a/src/utilities.lisp b/src/utilities.lisp
index 1670f55..82a387b 100644
--- a/src/utilities.lisp
+++ b/src/utilities.lisp
@@ -210,8 +210,10 @@
 ;;;--------------------------------------------------------------------------
 ;;; Locatives.
 
-(export '(loc locp))
-(defstruct (loc (:predicate locp) (:constructor make-loc (reader writer)))
+(export '(locative locativep))
+(defstruct (locative (:predicate locativep)
+		     (:constructor make-locative (reader writer))
+		     (:conc-name loc-))
   "Locative data type.  See `locf' and `ref'."
   (reader nil :type function)
   (writer nil :type function))
@@ -228,8 +230,8 @@
       (valtmps valforms newtmps setform getform)
       (get-setf-expansion place env)
     `(let* (,@(mapcar #'list valtmps valforms))
-       (make-loc (lambda () ,getform)
-		 (lambda (,@newtmps) ,setform)))))
+       (make-locative (lambda () ,getform)
+		      (lambda (,@newtmps) ,setform)))))
 
 (export 'ref)
 (declaim (inline ref (setf ref)))
@@ -451,6 +453,25 @@
    and return the result of appending all of the resulting lists."
   (reduce #'append (apply #'mapcar function list more-lists) :from-end t))
 
+(export 'cross-product)
+(defun cross-product (&rest pieces)
+  "Return the cross product of the PIECES.
+
+   Each arguments may be a list, or a (non-nil) atom, which is equivalent to
+   a singleton list containing just that atom.  Return a list of all possible
+   lists which can be constructed by taking one item from each argument list
+   in turn, in an arbitrary order."
+  (reduce (lambda (piece tails)
+	    (mapcan (lambda (tail)
+		      (mapcar (lambda (head)
+				(cons head tail))
+			      (if (listp piece) piece
+				  (list piece))))
+		    tails))
+	  pieces
+	  :from-end t
+	  :initial-value '(nil)))
+
 (export 'distinguished-point-shortest-paths)
 (defun distinguished-point-shortest-paths (root neighbours-func)
   "Moderately efficient shortest-paths-from-root computation.